Design and Synthesis of Stable Cobalt-Based Weak Ferromagnetic Framework with Large Spin Canting Angle

Abstract

It still remains a great challenge to design and construct framework-structured weak ferromagnets with large canting angle which is an effective approach for high performance magnets. According to the strategy of antisymmetric interaction causing spin canting, we report the design of four cobalt compounds, which were tested by X-ray single crystal diffraction, TGA, PXRD, and magnetic measurement. Single-crystal structure analysis reveals that compound 1 has a 2D structure, complex 2 has a 3,4-connected 3D framework, and complex 3 exhibits a 3D net structure with rare 3,5-connected 2-nodal β-SnF2 topology and the solvent MeOH trapped in the 3D channels as guests. The magnetic property of 3 is spin canting just as designed, with TN about 4.0 K and large canting angle of 14.8°. Highly stable compound 3 sustains its framework in air for more than 12 months, in which the guest MeOH molecules can be replaced by water to form complex 4.

Two Metal–Organic Frameworks Based on Hexanuclear Cobalt–Hydroxyl Clusters or a Manganese–Hydroxyl Chain from Triangular [MII3(μ3-OH)] (M = Co and Mn) Units: Antiferromagnetic and Spin-Canting Antiferromagnetic Ordering with Soft-Magnetic Behavior

“…The χ′ curves show peaks at 2.5 K, which indicate that there exists long-range ordering in compound 2 . While the peaks of χ″ are unsymmetrical and have a weak frequency dependence, which is consistent with the reported canting systems reported recently …”

“…While the peaks of χ″ are unsymmetrical and have a weak frequency dependence, which is consistent with the reported canting systems reported recently. 51 The field-dependent magnetization curve at 2 K (Figure 4b) shows a rapid increase in M under a very low field and reaches 2.64 Nβ at 2.0 T, further confirming the existence of spincanting behavior in compound 2. The curve shows a linear variation in the high-field region, and its value is 5.58 Nβ at 7.0 T, which is far less than the total alignment of the spin saturation (M s ) value of 30 Nβ for the expected {Mn II 6 } cluster.…”

“…For compound 2 , the χ m T value at 300 K is 23.12 cm 3 mol –1 K (Figure a), which is lower than the expected value of six isolated Mn II ions (26.25 cm 3 K mol –1 , g = 2.0, S = 5 / 2 ), indicating the presence of antiferromagnetic coupling between the Mn II ions. , On lowering the temperature, it decreased and reached a minimum of 4.44 cm 3 mol –1 K at 7.0 K prior to abruptly increasing to 15.96 cm 3 mol –1 K at 2.5 K. These features are indicative of spin-canting behavior. , The χ m T values at low temperature suggest a nonzero spin ground state, and the value at the 2.5 K suggests a S = 5 ground state. The fitting above 100 K for the χ m –1 vs T plot with Curie–Weiss law results in θ = −73.23 K and C = 28.82 cm 3 mol –1 K, which indicates a dominant antiferromagnetic interaction in compound 2 .…”

“…M s = ngSNβ = 6 × 1.9 × 2.5 Nβ, where S = 5 / 2 and g is calculated from the Curie constant). 51,54 Our previous reported WMOF-1 showed antiferromagnetic behavior, while in compound 2 there exists unusual spincanting antiferromagnetic ordering with a soft magnetic property. Analyzing the structrue, the triangular {Mn 3 O} units with syn−syn carboxylate bridges within the two compounds usually mediate antiferromagnetic coupling between the metal centers.…”

“…48,49 On lowering the temperature, it decreased and reached a minimum of 4.44 cm 3 mol −1 K at 7.0 K prior to abruptly increasing to 15.96 cm 3 mol −1 K at 2.5 K. These features are indicative of spin-canting behavior. 50,51 The χ m T values at low temperature suggest a nonzero spin ground state, and the value at the 2.5 K suggests a S = 5 ground state. The fitting above 100 K for the χ m −1 vs T plot with Curie−Weiss law results in θ = −73.23 K and C = 28.82 cm 3 mol −1 K, which indicates a dominant antiferromagnetic interaction in compound 2.…”